Ferrite with constricted magnetic hysteresis loop



June 20, 1961 o. EcKERT 2,989,479

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United States Patent 2,989,479 FERRIIE WITH CONSTRICTED MAGNETIC HYSTERESIS LOOP Oskar Eckert, Lauf (Pegnitz), Germany, assignor to Steatit-Magnesia Aktiengesellschaft, Lauf (Pegmtz),

Germany, a corporation of Germany Filed Nov. 26, 1956, Ser. Nb. 624,272 Claims priority, application Germany Nov. 25, 1955 2 Claims. (Cl. 252-;625)

Ferromagnetic metals with constricted hysteresis loops, (see, for example, Bozorth, Ferromagnetism, by Van Nostrand Co., Inc., 1951, pages 498 to `499), hasas is well known, at small field strength within the constriction area, constant permeability, i.e., permeability independent of the field strength equal to the initial permeability, very low hysteresis losses and, in general, small residual losses. As indicated in the. above-cited literature, such materials may be subjected to thermo-magnetic treatment. By thermomagnetic treatment, in this connection, is meant the passing thru a thermic cycle during the simultaneous presence of a magnetic longitudinal or transverse field. The concept of longitudinal or transverse field is, in this connection, to be understood as relative to the later measuring field; a longitudinal or transverse field, respectively, means that such field, during the thermomagnetic treatment, is parallel, respectively vertical, to the later measuring field. Thru this type of treatment, these ferromagnetic materials display a substantial alteration of the form of the hysteresis loop, and hence a change of the magnetic properties.

This invention is based on the discovery that it is possible to produce specific ferrites showing a constricted magnetic hysteresis loop which are, consequently, capable of thermomagnetic treatment similarly as for metals.

The invention teaches the production of such ferrites of the magnesium-copper-ferrite-system which can be subjected to thermomagnetic treatment of the above type, and are distinguished from hitherto familiar ferrites by the fact that, under the same manufacturing conditions, they have constricted hysteresis loops.

In accordance with the invention, ferrites with this characteristic in the magnesium-copper-ferrite-system must have a composition of at least 50 mol-percent Fe203, and a small addition of cobalt oxide. The addition of cobalt oxide is suitably determined between 0.1 and by weight, calculated on the total basic batch of the magnesium-copper-ferrite, expressed in metallic oxides. The invention has shown that it is particularly advantageous to choose the cobalt oxide content between 0.35 and 1.5% by weight, calculated on the basic batch. The magnesiumcopper-ferrites in question, which react strongly to the addition of cobalt oxide with a constricted loop, cover, in the three-component system FezOg--MgOf-CuO the area defined in the attached diagram FIG. 3 by the quadrangle A, B, C, D. The compositions at the corners for the system Fe2O3--MgO-Cu0 in percent by weight, are:

FezOa MgO CuO 2,989,479, Patented` June 20, 1.96.1

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extruding, or similar methods, or it may be desirable, before ceramic forming, to proceed with aY calcining firing, either of the entire mass or only a part thereof, preferably between 750 C. and 1250 C. The formed parts are sintered, depending on the composition, at temperatures between 1250 C. and 1400 C. To` produce the constricted hysteresis loop in ferrites in accordance with invention, it is necessary that the cooling takesv place slowly, particularly in the temperature range .between 700 C. and room temperature. The cooling speed isrdependent upon the volume of the fired body. As a criterion, it may be stated that for a ring of about 4.6mm. outside diameter, 34 mm. inside diameter, and 10 mm. height, the cooling time from 700 C. to room temperature should take not less than 12 hours. vIf the rings are cooled rapidly, the effect of loop constriction does not occur. However, the constriction may be regained even for rings cooled too rapidly, by re-heating them to a temperature of about 700 C., and cooling them slowly, as above described. Y A

An example of the invention follows hereafter:

ln a steel ball mill are ground together 412.5 g. Fe203, 62.5 g. MgO, 25.0 g. CuO, 3.25 g. CoO. After 6 hours of grinding, the slip is poured through a 4900 mesh screen (4900 meshes per square cm.) into a porcelain dish, and dried. The powder thus obtained, is pressed according to ceramic pressing techniques, into rings having dimensions of 59 mm. outside diameter, 35.8 mm. inside diameter, and 12 mm. height, the amount of pressure applied being about 0.5 to l t./cm.2. The ferrite pieces, thus obtained, are sintered in a kiln at 1370 C. for two hours, whereupon the heat is shut off. The rings are cooled to room temperature in the kiln during a period of approximately 24 hours. The ferrite rings thus obtained are provided with 0.4 mm. copper enameled wire with windings as primary winding, and, as secondary winding, further 200 wings with 0.2 mm, copper enameled wire are applied. The oscillographic photograph of this ferrite, produced in accordance with the invention, is shown in FIG. l; one can distinctly recognize the loop constriction of the hysteresis loop.

The following experiment proves that ferrites produced in accordance with the invention are susceptible to thermomagnetic treatment:

The ferrite toroid as prepared in the example, with 100 windings as a primary winding, is placed in a kiln. While heating to 600 C., and slow cooling for 12 hours to room temperature, a longitudinal magnetic field is maintained by means of the ring winding by 1 A direct current, corresponding to a magnetic field strength of about l5 A- windings/cm. If the hysteresis loop of the ferrite after this thermomagnetic treatment is recorded in the same manner as described above, the result is analogous to that of metals when they are subjected to heat treatment in the longitudinal magnetic field; a complete change of the form of the hysteresis loop takes place, as may be seen in FIG. 2. In analogous manner, heat treatment in the transverse magnetic field may be carried out with corresponding effect (see the above-cited book by Bozorth).

The technical progress obtained with such ferrites in accordance with the invention, may be seen in the following: with thermic longitudinal magnetization, for example, ferrites with distinctly rectangular hysteresis loop may be produced which are of importance to the entire fields of electronics and for magnetic amplification, for telephone and high-frequency fields; with thermic cross magnetization, ferrites of high quality and a permeability independent of field strength may be produced, which are particularly suitable for the field of telecommunication.

I claim:

1. A process of making a cobalt-modified, magnesitmcopper ferrite with a constricted hysteresis loop comprising providing an intimately mixed powder composition consisting of 72.5 to 90% by weight of ferrie oxide with the remainder consisting essentially of metal oxides selected from the group consisting of MgO, CuO and mixtures thereof, the proportion of said oxides being selected so that the Fe303 is at least 50 mol percent of said mixture, incorporating 0.1 to 5% by weight of cobalt oxide into said powder composition, molding the resultant pow.

der composition to shape and `firing at about 1250 C. to 10 1400 7 C., and thereafter, slowly cooling the tired product from a temperature of 700 C. down to room temperature over a period of at least about 12 hours,

2. A fired cobalt-modied, magnesium-copper ferrite having a constricted hysteresis loop prepared by the proc- 15 ess of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,549,089 Hegyi Apr. 17, 1951 2,565,861 Leverenz etl al. Aug. 28, 1951 2,656,319 Berge Oct. 20, 1953 2,723,239 Harvey Nov. 8, 1955 4 2,736,708 Crowley Feb. 28, 1956 2,886,530 Greger May 12, 1959 FOREIGN PATENTS 645,056 Great Britain Oct. 25, 1950 1,125,577 France July 16, 1956 1,129,275 France Sept. 3, 1956 OTHER REFERENCES I. Institute of Electrical Engineers, Japan, November 1937, pages 4, 5, 7; October 1939, page 571; June 1939, pages 276-279, 281.

Gorter: Proceedings of the IRE, December 1955, page 1961.

Weil: Comptes Rendus, v. 234, pages 1351, 1352 (1952).

Bozorth et al.: Physical Review, September 15, 1955, pages 1792, 1793.

Proceedings of the I.R.E., vol. 44, No. 10 (Ferrites 20 Issue), October 1956, pages 1300, 1301, 1304, 1305 and Ferromagnetism, Bozorth, D. Van Nostrand (1951), pages 498 and 499.

RCA Review, September 1950, page 345. 

1. A PROCESS OF MAKING A COBALT-MODIFIED, MAGNESIUMCOPPER FERRITE WITH A CONSTRICTED HYSTERESIS LOOP COMPRISING PROVIDING AN INTIMATELY MIXED POWDER COMPOSITION CONSISTING OF 72.5 TO 90% BY WEIGHT OF FERRIC OXIDE WITH THE REMAINDER CONSISTING ESSENTIALLY OF METAL OXIDES SELECTED FROM THE GROUP CONSISTING OF MGO, CUO AND MIXTURES THEREOF, THE PROPORTION OF SAID OXIDES BEING SELECTED SO THAT THE FE2O3 IS AT LEAST 50 MOL PERCENT OF SAID MIXTURE, INCORPORATING 0.1 TO 5% BY WEIGHT OF COBALT OXIDE INTO SAID POWDER COMPOSITION, MOLDING THE RESULTANT POWDER COMPOSITION TO SHAPE AND FIRING AT ABOUT 1250* C. TO 1400* C., AND THEREAFTER, SLOWLY COOLING THE FIRED PRODUCT FROM A TEMPERATURE OF 700* C. DOWN TO ROOM TEMPERATURE OVER A PERIOD OF AT LEAST ABOUT 12 HOURS. 